This patent application describes a novel invention related to data compression. The invention described herein relates to the insertion of data into a previously encoded bit stream and to the extraction of such data. The data may be related or unrelated to the content of the previously encoded bit stream.
The subject matter disclosed here may find particular application in the fields of broadcast and consumer audio. Modern distribution of audio signals to consumers involves the use of data rate reduction or audio compression techniques to lower the required amount of data required to deliver audio signals to consumers while causing minimal impact to the original audio quality. The reduction in the size of the data translates into savings of transmission and storage bandwidth, thereby allowing cost savings and/or carriage of more programs in a given space.
Systems including AC-3, DTS, MPEG-2, AAC and AAC-HE are examples of common audio data reduction techniques. For the purposes of this application, the AC-3 system will be used as an example, but the invention may be applicable to any codec system, audio or video.
Audio data compression lowers the amount of data required for transmission and/or storage of a given audio quality target. The resulting data produced by the compression process depends on the input audio and the audio quality target and, as such, it's data rate varies over time. Unused null, stuffing, or dummy bits may be inserted to maintain a constant output rate.
This unused data space may be used to carry additional data. This technique is described in U.S. Pat. No. 6,807,528 (“Adding Data to a Compressed Data Frame”) . A drawback of this approach is that continuous extra data may not always be available.